If Andy Murray's luck was out in Indian Wells, it has most certainly been with him in Miami.

The withdrawal last night of Rafael Nadal with a left knee injury, shortly before their scheduled semi-final, sent Murray into the final of the Sony Ericsson Open for the second time.

The Scot will take on the winner of last night's second semi-final between world No.1 Novak Djokovic of Serbia and Juan Monaco of Argentina.

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And though part of him will have been disappointed not to take on Nadal and hopefully beat him, there will also have been relief that he did not have to over-exert himself before a potential showdown with Djokovic for the title.

Murray has led a charmed life in Miami these past 10 days, beginning with the walkover he received into round four, when Milos Raonic pulled out through injury.

Nadal's knee problem flared up after his fourth-round win over Kei Nishikori of Japan and after beating Jo-Wilfried Tsonga in the quarter-finals, he admitted that he may struggle to be fully ready to take on Murray.

The world No.2 waited until the morning of the match to give the knee a final test, texting Murray to tell him the news before the two men met briefly in the locker-room.

"I am not ready to compete today," he said. "I am very sorry for the fans. I'm very sorry for the tournament. I'm very sorry for everybody who was ready to watch the match on television. I cannot go on court and lie to everybody."

The Spaniard said he first felt the problem before Indian Wells earlier this month, but said he believed he would be fully fit for the start of the clay-court season in Monte Carlo, the week after next.

"This year, I started well with no problems. Today is bad news, but that's the sport," Nadal said.

"We cannot expect playing as much as we play to be perfect every day of our life. Today is my turn. Everybody has problems, and I will be working hard to be back quick on court and to play my best in Monte Carlo."

While Murray went off to refine his practice ahead of a meeting with Djokovic or Monaco, the women's finalists, Maria Sharapova and Agnieszka Radwanska, were also hard at work ahead of today's showdown.

Both women will be glad that Victoria Azarenka is not their opponent – the Belarussian is the only woman to beat Radwanska in 2012, while she also denied Sharapova in the final of the Australian Open.

For world No.4 Radwanska, it is a chance to win a first big title, but for Sharapova there is the opportunity to increase momentum in a renaissance that has had everything but a grand slam title.

Ever since she turned professional on her 14th birthday, the Russian has never been too far out of the limelight, winning Wimbledon at 17 and adding two more grand slam titles. But over the past 18 months, there has been more talk of others; was Caroline Wozniacki a worthy world No 1?; could Azarenka make the step up?; how many Wimbledon titles will Petra Kvitova win?

Now, after one of the most consistent years of her career, Sharapova is back in the spotlight again. Victory over Radwanska would push her closer to Azarenka at the top and confirm that she really is back.

"When I play well, I'm an aggressive player," she said after her semi-final win over Wozniacki. "I go for my shots. I don't hesitate."

After serious shoulder surgery in 2008, Sharapova missed most of 2009 and was unable to play in Miami in 2010 because of an elbow injury.

Last year's run to the final – when she lost to Azarenka – was the start of her resurgence and having spent most of her tennis-playing youth at the nearby Nick Bollettieri Academy, Sharapova would dearly love to win the title for the first time, having lost in the final three times. Sharapova leads 7-1 in head-to-head meetings with Radwanska, but knows history will count for little.

"She is someone who is extremely solid, gets many balls back and anticipates really well," she said. "But it's the final so I think it's more about performing on your end than really worrying about what's on the other side of the court."